In recent years, a so-called self-luminous display device is attracting attention, which has pixels each including a light-emitting element such as a light-emitting diode (LED). As the light-emitting element used for such a self-luminous display device, an organic light-emitting diode (also referred to as an OLED, an organic EL element, an electroluminescence: EL element and the like) is attracting attention, and is becoming to be used for an organic EL display.
The light-emitting element such as an OLED is a self-luminous type; therefore, it has such advantages that the visibility of pixels is high, no back light is required and high response rate is attained as compared to a liquid crystal display. In addition, the luminance of the light-emitting element is controlled by a current value flowing thereto. Therefore, in order to display gray scales accurately, there has been proposed a display device using a constant current drive where a constant current is supplied to the light-emitting element (see Patent Document 1).    [Patent Document 1] Japanese Patent Laid-Open No. 2003-323159